The use of different copolyesters and copolyetheresters is described at length in the literature.
DE 196 32 473 and DE 196 32 474 describe fast crystallizing and highly-flexible copolyetherester hot-melt adhesives based on terephthalic acid, butane-1,4-diol, diethylene glycol, triethylene diol and polyethylene glycol. These copolyetheresters crystallize very fast at a melting point of over 115.degree. C. The lower-melting polyesters, having a melting point of about 90.degree. C., are not suitable for adhesive use as a film, web or powder due to their lower crystallization speed and the associated stickiness.
EP 698 648 describes low-melting copolyesters having a melting point of 60-130.degree. C. for the hot-melt adhesive range. These polyesters are based on terephthalic acid, isophthalic acid, butane-1,4-diol, diethylene glycol and triethylene glycol. Ensuing from this monomer composition is the sole fact that the crystallization speed is far too low to justify the claims set forth in this document.
JP 59 011 383 describes polyesters for hot-melt PVC bonding adhesives having melting points of 80-160.degree. C., comprising terephthalic acid, adipic acid, butane diol and diethylene glycol. This combination also yields an insufficient crystallization speed.
CH 618199 describes numerous copolyesters and their compositions, the copolyesters having melting points of 50-200.degree. C. The crystallization behavior, however, is characterized as very slow.
Finally, U.S. Pat. No. 4,551,521 describes low-melting polyester adhesives having melting points of 60-130.degree. C. These polyesters primarily comprise adipic acid and cyclohexane dimethanol, and readily fulfill the criterion of a high crystallization speed. In contrast to the polyesters and copolyetheresters of the present invention, however, the polyesters are completely aliphatic; in other words, no terephthalic acid is used. Completely-aliphatic polyesters have excellent biodegradability, but are therefore naturally susceptible to weather influences and moisture. This property is counterproductive for a hot-melt adhesive that is intended to connect two substrates and must possess a certain resistance to heat. According to the invention, the greater biodegradability is assured up to a 30% proportion of aromatic components.
All of the copolyesters or copolyetheresters described in the prior art are associated with significant drawbacks, and do not yield thermoplastic copolyester or copolyetherester hot-melt adhesive masses having the low melting point, high crystallization speed, high flexibility and chemical stability that would make them suitable for use as hot-melt adhesives in technical applications for difficult substrates.
Thus, a need exists for developing quick-crystallizing and lightly-flexible products, having maximum melting temperatures of 100.degree. C., for hot-melt adhesive applications.